1. Field of the Invention
The present invention relates to a catalyst and process for reverse disproportionation of ethylene and stilbene to produce styrene. The catalyst comprises tungsten, cobalt, and an alkali or alkaline earth component on a support, preferably silica gel.
2. Description of the Prior Art
The production of styrene from stilbene and ethylene is disclosed in U.S. Pat. No. 3,965,206, the teachings of which are incorporated by reference. Use of conventional disproportionation catalysts such as cobalt molybdate on alumina, or tungsten oxide or silica, alumina or silica-alumina, for reverse disproportionation is taught.
U.S. Pat. No. 3,764,635, Fattore, et al, the teachings of which are incorporated by reference, teaches a process for disproportionating olefins using a catalyst of tungsten and bismuth on a support, preferably silica. The catalyst is active for disproportionation without any activation step.
U.S. Pat. No. 3,792,107, Fattore, et al, the teachings of which are incorporated by reference, discloses use of a catalyst of tungsten and copper or tungsten and Group VIII metals, preferably Fe, Co, or Ni, on silica or other support. The ratio of added metal to tungsten taught is 1:3 to 5:1, although all examples show use of a 1:1 metal:tungsten ratio. It is claimed that this catalyst requires no activation before use in disproportionation.
U.S. Pat. No. 3,728,414, Helden, et al, the teachings of which are incorporated by reference, teaches a conventional olefin disproportionation catalyst with a promoter, a Group IIIa metal on an alumina carrier. Conventional olefin disproportionation catalysts are said to contain titanium, vanadium, chromium, manganese, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, tin, hafnium, tantalum, tungsten, rhenium, osmium, and iridium. This reference teaches that additional components, e.g., coactivators, hydrogenating components, components for isomerization of the double bond, and the like may also be added. Coactivators listed include cobalt oxide, and compounds of iron, nickel, and bismuth.
U.S. Pat. No. 4,192,961 teaches conversion of a mixture of dibenzyl and stilbene with ethylene in the presence of a catalyst of chromium oxide, tungsten oxide, an oxide of an alkali metal and silica or alumisilicate. Styrene yields of 78 to 80 wt %, based upon conversion of ethylbenzene, dibenzyl, and stilbene, are claimed.
U.S. Pat. No. 3,658,930, Kenton, et al, the teachings of which are incorporated by reference, teaches disproportionation of olefins using a rhodium oxide promoter on conventional olefin disproportionation catalyst, e.g., tungsten, molybdenum, rhenium, or tellurium on silica.
U.K. patent specification No. 1,205,677 teaches disproportionation of olefins using a conventional catalyst, such as molybdenum trioxide, tungsten trioxide, or rhenium heptoxide on alumina, silica, or alumina-silica, and incorporating into this conventional catalyst a second component to effect double bond isomerization of olefins. Group VIII noble metals are suggested as being suitable, with preferred isomerization catalysts containing platinum and especially palladium. An alkali or alkaline earth metal ions are added to the catalyst to serve as a base to inhibit the oligomerization of branched chain olefins.
None of these prior art catalysts are believed to possess sufficient activity and stability to permit their use in a commercial reverse disproportionation process.
Another failing of most prior art catalysts is that a relatively high temperature activation procedure is necessary before the catalysts are suitable for use. These catalysts are extremely active, but have very short lives before carbon and coke deposition destroys catalytic activity. Frequent regeneration and activation of the catalyst are necessary for a successful commercial process. It is desirable to minimize stress on the catalyst and on the equipment by eliminating large temperature swings necessary for activation and regeneration of the catalyst. It is also desirable if the catalyst has great stability and is able to operate for relatively long periods.